The US climates which would probably most closely approximate the conditions you seem to be describing would be our southern states, such as Florida and along the Gulf Coast. Typically, the types which flourish in those climates with the least amount of chemical spraying for diseases tend to be the Noisettes, Chinas and Teas (not Hybrid Teas). I don't know if any of these might be suitable for your cut flower business.

What have been the issues you have encountered which have limited your success? Generally, rose species are indigenous to more northern latitudes, temperate to sub arctic. Roses growing below their natural range and any in the Southern Hemisphere, grow there because they have been taken there. They do not occur in those latitudes naturally. I would think the disease pressures where you are attempting to grow them should be rather high due to the humidity and rainfall totals.